1. Technical Field
The present principles generally relate to anti-jamming coding techniques for cognitive radio systems, and, more particularly, to anti-jamming coding methods and systems including retransmission protocols.
2. Description of the Related Art
Recently, cognitive radio has drawn significant interest due to the congestion of unlicensed frequency bands in many countries throughout the world. Cognitive radio techniques are based on the concept of spectrum under-utilization, in which licensed frequency bands are rarely utilized to its maximum potential by licensed users. Indeed, among licensed bandwidth users, there is very little usage on a very large range of spectrum in both time and space. Cognitive radio is therefore a promising solution that aims to introduce secondary, low priority usage of licensed spectrum resources while ensuring that primary usage by licensed users is not interfered with. In accordance with some known cognitive radio systems, such opportunistic spectrum sharing is provided by employing spectrum sensing systems that dynamically identify spectrum bands in which primary users are not active and permit utilization of these spectrum white spaces by secondary users.
As mentioned above, an important constraint in cognitive radio is that the secondary users should not interfere with primary users. Typically, the primary users are not aware of the existence of the secondary users. When a primary user begins signal transmission through channels employed by a secondary user, the secondary user immediately discontinues transmission along these channels and switches to other available channels. Because such interference periods are short, they do not impair the communication of a primary user. However, during these periods, the signals of a secondary user are corrupted by strong interference from the primary user, as a secondary user usually operates with low power profiles to minimize any interference with primary user transmission. Such collision is also commonly referred to as jamming. To reduce packet loss instances and maintain the communication reliability for secondary users, anti-jamming coding techniques are desirable for cognitive radio systems.
With reference to FIG. 1, anti-jamming coding schemes have been studied using a cognitive radio system model in which information and messages are transmitted by secondary users through many parallel subchannels. The cognitive radio system model depicted in FIG. 1 is described in more detail below. Despite the limited success of known anti-jamming coding techniques, packet or information loss nevertheless occurs. To the knowledge of the inventors, retransmission protocols for un-recovered packets and/or information have not been incorporated within anti-jamming coding techniques.
However, retransmission schemes associated with coding in general have been extensively considered with regard to Gaussian or fading channels in relation to hybrid automatic transmission requests in Automatic Repeat Query (ARQ) schemes. Further, ARQ schemes have been studied in systems using multiple parallel channels. These ARQ schemes, however, fail to incorporate ARQ considerations with channel coding.
As discussed above, existing anti-jamming coding techniques for cognitive radio systems fail to incorporate retransmission protocols. Thus, a need exists for effective anti-jamming coding methods and systems including retransmission protocols to address inherent information loss resulting from packet non-recovery due to interference from primary users or other transmission interference sources.